1. Technical Field of the Invention
This invention relates generally to mixed signal circuitry and more particularly to clocking circuits that may be used within a wireless communication device.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
As is further known, the local oscillation generator produces the local oscillations of the transmitter section and receiver section. Typically, the local oscillation generator includes a phase locked loop to produce an output oscillation from a reference oscillation. One known embodiment of a local oscillation generator includes a buffer, or multiple buffers, coupled to the output of the phase locked loop to produce the local oscillations for the transmitter section and the receiver section. Another known embodiment of a local oscillation includes a divide by two module and a summation module to produce the local oscillations. In this embodiment, the divide by two module divides the frequency of the output oscillation by two to produce a one-half output oscillation. The summation module sums the output oscillation with the one-half output oscillation to produce an oscillation at the desired frequency of the local oscillations.
As is also known, noise generated within the local oscillation generator is propagated throughout the transmitter section and the receiver section. As such, great care is taken to reduce the noise generated by the local oscillation generator and the phase locked loop contained therein. For instance, many local oscillation generators include differential signaling to reduce the adverse affects of common mode supply noise. In addition, the power supply sourcing the phase locked loop may include filtering to reduce of the adverse affects of supply voltage noise. While each of these techniques reduces the noise produced by a local oscillation generator, there is still room for improvement.
Therefore, a need exists for a phase locked loop with distributed power to reduce noise therein and, if used in a local oscillation generator, to reduce the noise of the local oscillation generator.